The present disclosure relates to the fabrication of micro structures and micro devices.
Sacrificial material is commonly used to fabricate micro devices. Planar micro fabrication technologies usually build micro structures in layers over a substrate, such as in a bottom up manner. The lower layers are deposited and processed, followed by the upper layers. Sacrificial material can be used when a micro structure includes an air gap between an upper structure portion and a lower structure portion. The sacrificial material is disposed over the lower structure portion. The upper structure portion is subsequently formed over the sacrificial material and the lower structure portion. The sacrificial material is finally removed to form the air gap between the upper structure portion and the lower structure portion. Photoresist is a commonly used sacrificial material.
There are several drawbacks to using photoresist as a sacrificial material. Photoresist is not stable above 150° C., which prevents the use of any processing steps at temperatures over 150° C. after applying the photoresist sacrificial material. The hardened photoresist has limited mechanical strength; it often cannot provide enough mechanical support for the upper structure portion, particularly if the upper structure portion is thin. Without proper mechanical support from the hardened photoresist, a thin upper structure portion may not be able to sustain mechanical stresses during processing, such as chemical mechanical polishing (CMP). Furthermore, photoresist usually has impurities such as oxygen or nitrogen, which may cause contamination in certain device applications.